Asphalt release coating



United States Patent ffiee 2,916,466 Patented Dec. 8, 1959 ASPHALT RELEASE COATING Richard J, Rother, Sr., St. Ann, and Albert R. McManus,

St. Louis, Mo., assignors to Crown Zellerbach Corporation, San Francisco, Calif., a corporation of Nevada N Drawing. Application February 6, 1957 Serial No. 638,449

2 Claims. (Cl. 260-17.4)

This invention relates to a coating composition for application to the interior surface of expendable paperboard containers for shipping and storing materials which tend to adhere to the container walls.

The invention is an improvement of the release coating of Richard J. Rother and Albert R. McManus, disclosed in Patent No. 2,672,454 which issued March 16, 1954.

The usual practice in preparing asphalt, for example, for shipment and storage in containers is to render it readily flowable by raising its temperature to from 250" F. to 400 F. or even higher and rapidly pouring it into containers which are then allowed to stand until the asphalt solidifies. Packages for this purpose have been made of thin gauge metal, paperboard, or other suitable materials. However, since the packaging of asphalt for roofing purposes, manufacture of shingles and many other purposes is a large-scale operation, the storage of metal drums and other non-collapsible containers entails a storage space problem of considerable magnitude. Paperboard containers consequently have important advantages over metal containers due to their lower cost and the fact that they may be shipped to the user and stored in collapsed form, requiring a minimum of storage space prior to transfer to the loading line.

The use of paperboard containers for packaging materials of the class described involves difiioult problems since these materials in their liquid form tend to penetrate paperboard, so that in the absence of an effective barrier between the walls of the container and the hot materials, leakage of the latter may result. In addition such materials are quite tacky at elevated temperatures and strongly adhere to paperboard so that it is impossible to strip the containers from the solidified contents without leaving highly objectionable adhering strips, slivers and particles of paperboard embedded therein. Such extraneous materials render asphalt, for example entirely unsuitable for the purpose hereinbefore described.

Many prior types of coating when applied to the flat blanks from which the containers are formed have a tendency to crack or flake at the scores when the blank is scored and assembled and allow the fluid material to penetrate and strongly adhere to the board at the score lines with the consequence that strips, slivers and particles of the latter remain embedded in the solidified asphalt when the container is removed therefrom. Further there is a tendency under certain conditions to migration of some of the asphalt components into the paperboard with resulting interference to a clean stripping from the asphalt at the point of use.

The coating of the present invention is especially designed to render the interior surface of paperboard impervious to materials such as asphalt, tar, pitches and other materials which are introduced into the container at elevated temperatures and solidify upon cooling. The coating, moreover, forms a strong bond with the packaged materials of the class described and a relatively weak bond with the paperboard, so that when the contents becomes solidified, the container may be readily stripped therefrom, leaving the material entirely free of the paperboard slivers, fragments and the like. Furthermore, the coating retained by the asphalt is entirely free of any detrimental effect on the asphalt for the purposes hereinbefore described.

Continuous large volume use of the coating disclosed in the hereinbefore referred to Patent No. 2,672,454, while generally satisfactory, has shown that the said coating may occasionally under some conditions tend to crack or flake to some extent at the score lines when the scored coated blank is assembled, thereby permitting some undesirable penetration of the asphalt along the scores into the paperboard. Also at certain times there may be an undesirable migration of some of the components of the asphalt into the walls of the paperboard container, tending to interfere with the desired perfectly clean release of the container from the solidied asphalt, particularly when the asphalt is introduced at temperatures above 325 F. to 350 F. These deficiencies, in the aforesaid patent, while occurring only occasionally, nevertheless entail a highly objectionable hand labor and time consuming operation for salvaging the contaminated asphalt by removing therefrom slivers and particles of paperboard.

The present invention completely overcomes these occasional but comparatively rare objectionable occurrences of the release coating of the said patent. The subject coating film is of substantially improved elasticity and completely eliminates any tendency to cracking, flaking or partial failure at the scores even when the asphalt is poured at temperatures up to 400 F. which has become more or less standard practice in recent years for asphalt for certain purposes. Additionally and of equal or even greater importance, the coating of the present invention provides a barrier of marked improvement in resistance to migration of some of the asphalt components into the paperboard even at pouring temperatures up to 400 F. These improvements are of substantial practical importance to the large volume production line packaging system employed in the asphalt industry wherein complete freedom from contamination of the asphalt by paperboard particles is an essential feature of the packages.

A principal object therefore of the invention is to provide a release coating composition for applying to the inner surfaces of paperboard containers which effectually prevents penetration of asphalt and other bituminous and similar materials at elevated temperatures into and through the board and which adheres but slightly to the board so that upon solidification of the contents the container may be cleanly and readily removed, leaving the solidified material entirely free of paperboard particles.

Another object is to provide a release coating which may be applied to a flat blank which is scored and assembled into a container for packaging asphalt and other bituminous materials at elevated temperatures which is suiflciently elastic to permit folding of the blank without cracking, flaking or disruption of the continuous coating film upon assembling the container.

Still another object is to provide a release coating composition for the interior surface of the drum for packaging liquid asphalt which adheres to the asphalt upon stripping the container therefrom upon solidification and is entirely free of any detrimental effects to the asphalt for the use hereinbefore described.

A further object is to provide a release coating composition which may be applied in a single coat to the interior surfaces of a paperboard asphalt drum which upon cooling forms a very strong bond with the asphalt contained therein and a relatively weak bond to the paperboard.

A still further object is to provide a process for pre paring a composition suitable for coating the interior surface of paperboard containers for shipping and storing asphalt and other bituminous materials.

The coating consists of an aqueous composition of about 64% solids comprising the following ingredients, expressed in parts by weight, compounded in the order set forth:

Step I.-Into a tank of suitable size, equipped with agitation, preferably of a type designed to avoid entainment of air into the mixture, about 67 gallons of water are introduced at a temperature of about 125 F. to 150 F. or raised to that level after the introduction if means for heating the water in the tank is provided.

Step 2.-About 13 pounds of sodium alginate are dispersed in about 28 gallons of water and added to the tank and agitation of the mixture is started and continued throughout the additions and compounding of the subsequently added ingredients. It is preferred to use a form of sodium alginate of as low viscosity as possible. A satisfactory commercially available brand is marketed under the name of Kelgin XL, though other brands of the material may be used.

Step 3.-About 3 /2 pounds of sodium hydroxide dissolved in about 4 gallons of water are added to the circulating mixture.

Step 4.-Approximately 2000 pounds of a hydrous aluminum-silicate type of clay are sifted into the tank as rapidly as possible and the agitation continued until all lumps are broken down and a smooth, homogeneous mixture is attained. This will usually require 30 to 60 minutes, depending on the efficiency of the agitating equipment. About 4 or 5 gallons of water are used to rinse the agitator paddles free of the mixture. Suitable types of commercially available clays are known by the trade names Klondike, DRG and Kaolex.

Step 5.Approximately 537 pounds of an aqueous emulsion of a butadiene-acrylonitrile copolymer of the Buna-N type of synthetic rubber containing approximately 40% solids, then about 9 gallons of water are added and mixed for approximately one hour.

It is desirable that the ratio of the butadiene-acrylonitrile copolymer of the Buna-N type emulsion be held as closely as possible to about 57-59 parts butadiene to 43-41 parts acrylonitrile respectively for each 100 parts of the copolymer to insure the most satisfactory performance of the coating composition. One of the available commercial brands, known as Hycar No. 1561 of of about 40% solids content is very satisfactory.

The addition of the synthetic rubber emulsion cornpletes the preparation of the coating composition. The quantities set forth in steps 1 to 5 inclusive will produce approximately 292 gallons of coating composition having a solids content of 64% to 65%. The pH of the composition will be between 10.0 and 10.5.

The composition may be given a distinctive color if desired by incorporating a dye therein, preferably following step 1 of the process and before the addition of the sodium alginate. For example about 16 /2 pounds of a black dye may be dissolved in the initial charge of water. A suitable dye for the purpose is nigrosine WSB, but various other water soluble dyestuffs may be employed if desired.

The coating dries on the paperboard rapidly and may be readily applied to the blank by spraying, brush or other convenient means, but is preferably applied to the unscored roll stock on the standard coating machine.

The subject coating is the result of several years of extensive research coupled with field tests to improve the elasticity of the applied film of coating sufficiently to completely eliminate cracking and flaking at the scores of the assembled paperboard blank and concurrently adequately improve the barrier it provides to penetration not only of the hot asphalt but more particularly to eliminate the migration of any component of the asphalt into the paperboard to meet the requirements of the large scale production line operations employed in the asphalt industry.

The invention therefore permits the forming of a novel paperboard package of asphalt adapted for shipping and storage. The interior surfaces of the paperboard container is coated with a continuous film of an aqueous latex coating composition which effectually inhibits cracking or flaking of the film throughout the folded scores forming the container. Furthermore, the coating not only forms an effective barrier to the penetration of liquid asphalt and other bituminous materials but inhibits migration of any components thereof into the paperboard when the asphalt and other materials are introduced into the container at temperatures up to at least 400 F. Thus the package may be cleanly stripped from the solidified asphalt at the point of use leaving said asphalt completely free of contamination.

We claim:

1. A package of asphalt comprising a paperboard container initially filled with molten asphalt at a temperature of about at least 400 F. and solidified upon cooling, the interior surface of the container having a coating of a continuous film of a dried flexible release coating composition having the following characteristics; resistant to cracking or flaking of the coating film at all folded score lines of the container, resistant to penetration of asphalt and migration of any components thereof into the paperboard, whereby at the point of use the container may be readily and cleanly removed from the asphalt leaving the said asphalt, coated with the coating composition and free of contamination by extraneous matter from the paperboard container, said release coating composition preparatory to its application to the paperboard comprising initially the following admixed ingredients; about 113 gallons of water, about 13 pounds of sodium alginate, about 3 /2 pounds of sodium hydroxide, approximately 2000 pounds of hydrous aluminum-silicate clay and about 537 pounds of an aqueous emulsion of butadiene-acrylonitrilc copolymer of approximately 40% solids content in the ratio of about 57-59 parts of butadiene for each 43-41 parts respectively of acrylonitrile.

2. A coating composition for a foldable scored paperboard container initially filled with molten asphalt at a temperature of about 400 F. and solidified upon cooling, the coating applied to interior surface of the container as a continuous dried flexible releasable film having the following characteristics; being resistant to cracking or flaking of the coating film at all folded score lines of the container, resistant to penetration of asphalt and migration of any components thereof into the paperboard, whereby at the point of use the container may be readily and cleanly removed from the asphalt leaving the said asphalt, coated with the coating composition and free of contamination by extraneous matter from the paperboard container, said release coating composition comprising the following admixed ingredients; about 113 gallons of water, about 13 pounds of sodium alginate, about 3 /2 pounds of sodium hydroxide, approximately 2000 pounds of hydrous aluminum-silicate clay and about 537 pounds of an aqueous emulsion of butadiene-acrylonitrile copolymer of approximately 40% solids content in the ratio of about 57-59 parts of butadiene for each 43-41 parts respectively of acrylonitrile.

References Cited in the file of this patent UNITED STATES PATENTS 2,558,634 Uber June 26, 1951 2,662,040 Thomas Dec. 8, 1953 2,672,454 Rother et a1. Mar. 16, 1954 

2. A COATING COMPOSITION FOR A FOLDABLE SCORED PAPERBOARD CONTAINER INITIALLY FILLED WITH MOLTEN ASPHALT AT A TEMPERATURE OF ABOUT 400* F. AND SOLIDIFIED UPON COOLING, THE COATING APPLIED TO INTERIOR SURFACE OF THE CONTAINER AS A CONTINOUS DRIED FLEXIBLE REELEASABLE FILM HAVING THE FOLLOWING CHARACTERISTICS; BEING RESISTANT TO CRACKING OR FLAKING THE COATING FILM AT ALL FOLDED SCORE LINES OF THE CONTAINER, RESISTANT TO PENETRATING OF ASPHALT AND MIGRATION OF ANY COMPONENTS THEREOF INTO THE PAPERBOARD, WHEREBY AT THE POINT OF USE THE CONTAINER MAY BE READILY AND CLEANLY REMOVED FROM THE ASPHALT LEAVING THE SAID ASPHALT, COATED WITH THE COATING COMPOSITION AND FREE OF CONTAMINATION BY EXTRANEOUS MATTER FROM THE PAPERBOARD CONTAINER, SAID RELEASE COATING COMPOSITION COMPRISING THE FOLLOWING ADMIXED INGREDIENTS; ABOUT 113 GALLONS OF WATER, ABOUT 13 POUNDS OF SODIUM ALGINATE, ABOUT 31/2 POUNDS OF SODIUM HYDROXIDE, APPROXIMATELY 2000 POUNDS OF HYDROUS ALUMINUM-SILICATE CLAY AND ABOUTT 537 POUNDS OF AN AQUEOUS EMULSION OF BUTADIENE-ACRYLONITRILE COPOLYMER OF APPORXIMATELY 40% SOLIDS CONTENT IN THE RATIO OF ABOUT 57-59 PARTS OF BUTADIENE FOR EACH 43-41 PARTS RESPECTIVELY OF ACRYLONITRILE. 